Manes

In Romanmyth, Manes were ghosts. Their name could be taken from Mania, their mother, or from manare which means to flow. They literally swarmed through the underworld as bats or moths and lived there. If they ever escaped it was believed they would destroy the living world. The Romans kept them locked in the underworld by prayers, spells and sacrifices of blood. Eventually, people believed that unless family kept pictures of their dead relatives then those relatives would be cursed to join the Manes.

A monster in the Rogue-style game Nethack, represented by a red 'i'. Though individually a Manes is nearly as harmless as a grid bug, they come in large swarms which can very easily cause YASD. As with most swarms, the best response is to stand in a corridor so they can only come at you in single file.

An important thing to note is that 'Manes' is the singular as well as the plural. This is often misunderstood, understandably.